Microbial iron transport is under study. Many microorganisms excrete high affinity iron chelating agents which function as iron transport cofactors (siderophores). These chelating agents usually are secondary hydroxamates or derivatives of 2,3-dihydroxybenzoic acid. Previous work has shown that the ferrisiderophores are transported across the membrane to form a pool of available internal iron. An organism may use several different natural siderophores, and probably transport each by an independent system. Iron is released from the chelate for metabolism, and the iron-free deferrisiderophore is re-cycled. Current goals are, 1) to isolate the membrane bound and soluble components of the ferrisiderophore transport systems, 2) to isolate and examine the functions of the enzymes and essential factors required for release of iron from ferrisiderophores subsequent to their transport, 3) to identify the elements of this system which control transport of ferrisiderophores and synthesis of deferrisiderophore.